Magnetron shielding means



Feb. 28, 1967 N. A. PEEK 3,307,068

MAGNETRON SHIELDING MEANS Filed Oct. 24, 1963 .HGZ FIG.3.

FIG.4.

INVENITOR: NELSON A. PEEK,

HIS ATTORNEY.

3,307,068 MAGNETRON SHIELDING MEANS Nelson A. Peek, Rotterdam, N.Y., assignor to General Electric Company, a corporation of New York Filed on. 24, 1963,Se1-.No. 318,562 Claims. (Cl. 31539) This invention relates to shielding of exposed terminal connectors in R.F. apparatus generally, and more particularly to magnetron shielding specifically of the voltage tunable magnetron variety.

When direct current charges are applied from a high internal impedance power supply to a magnetron or other such component consisting of electrodes or voltage leads enclosed in a dielectric, current pulses appear during various operating conditions, particularly high altitude operation. Current pulses are produced by an electrical charge forming on the exterior surface of the dielectric due to a small but finite leakage current diffusing through the dielectric from the high voltage electrodes or leads. During high altitude operation or tests, for example, a critical pressure is reached which causes the electrical charge formed on the surfaces of the dielectric to flash over to an adjacent lead or other electrical conductor, thereby producing current pulses. In voltage tunable magnetrons this phenomenon, coupled with a high impedance power supply, causes very rapid voltage spikes to appear on the DC. leads, which in turn produces a frequency instability which cannot be tolerated in many applications.

Accordingly it is an object of this invention to provide improved shielding means for the terminals of RP. apparatus.

It is another object of this invention to provide improved voltage tunable magnetron shielding means for the terminals thereof.

It is a still further object of this invention to provide both terminal and lead shielding means in an improved manner in a voltage tunable magnetron assembly.

Briefly described, this invention in one preferred form is applied to a voltage tunable magnetron where the DC. input leads are eflectively shielded by covering their usual insulation with a further cover or coating of a predetermined electrical conductivity material, or by inserting a predetermined electrical conductivity material in a dielectric covering. In combination therewith, the exposed external terminal portions of the magnetron together with the connecting portions of the DC. leads are encased or encapsulated in a suitable dielectric material in which there is positioned an electrical conducting grid member electrically grounded.

This invention will be better understood when taken in connection with the following description and the drawings in which FIG. 1 is a partial sectional illustration of a preferred embodiment of this invention as practiced on a voltage tunable magnetron,

FIG. 2 is a top view of the terminal section of the magnetron of FIG. 1,

FIG. 3 is a bottom view of the magnetron of FIG. 1, and

FIG. 4 is an illustration of a cover assembly for the bottom of the magnetron of FIG. 1.

Referring now to FIG. 1, there is illustrated a voltage tunable magnetron assembly to which this invention is particularly applicable. Magnetron assembly 10 includes a central magnetron tube portion 11 which is contained in a mounting casing or structure 12. From structure '12 there extends an output coupler casing 13 which provides suitable output coupling to magnetron 11. Magnetron assembly 10 also includes an input lead assem- United States Patent 0 bly 14 comprising a plurality of individual D.C. leads 15, 16, 17 and 18, which are encased by and pass through an electrical insulating block or bushing 19. Block 19 is usually employed as a wall grommet to pass the mentioned leads through a suitable wall to be electrically connected to magnetron 11. Exemplary construction of the magnetron to which this invention is particularly applicable, and also the electrical connections thereto, are given in US. Patents 3,020,445 Weinstein and 3,020,446 Bessarab. For example, lead 15 passing through block 19 is usually connected to the cold cathode of the magnetron 11 while leads 16, 17 and 18 are connected to the heater cathode terminals and control terminal of the magnetron 11.

As best illustrated in FIG. 2, leads v16, 17 and 18 are connected to button-type terminals 20, 21 and 22 which project from the ceramic body 23 of magnetron 11. A suitable cup-shaped cavity member 24, as part of the structure 12, is disposed in surrounding relationship to the terminals 20, 21 and 22. Member 24, as further illustrated in FIG. 1, not only surrounds the projecting button terminals 20, 21 and 22, but also engages a portion of the ceramic body 23 about its periphery and extends upwardly a distance greater than the projection of the button terminals 20, 21 and 22. It has been discovered that the usual insulating means, as known in the art, when applied to the DC. input leads of a magnetron, for example those leads 15, 16, 17 and 18 as referred to in FIG. 1, and also to the terminals 20, 21 and 22, do not effectively electrically shield the magnetron assembly. When voltages are applied from a very high internal impedance power, flashover or corona problems occur not only during high altitude operation but also under certain conditions at sea level pressures. Because of a magnetrons exposure to varying pressure, temperature, and other environmental conditions, the insulating material for example in cup 24 will bleed ofi electrical charges by corona or arc discharge to ground. The varying conditions mentioned also cause the insulating material to expand and contract and thus to provide gaps between it and surrounding metal where arcing occurs. Therefore, proper electrical shielding is necessary in order that the magnetrons may be operated in very sensitive applications in which little if any frequency instability is permitted.

It has been further discovered that encapsulation of terminals of a voltage tunable magnetron, together with the use of an internal electrically conducting grid, effectively eliminates the corona and flashover problems as previously described. As one particular means of providing effective shielding or insulation between terminals 20, 21 and 22, an electrically conducting fine grid 25 is disposed Within cup-shaped member 24 and preferably in surrounding relationship to both the ceramic body 23 and terminals 20, 21 and 22. Furthermore, grid 25 is also radially spaced from ceramic body 23 and the up standing wall portion of cup-shaped member 24. In one preferred and operative practice of this invention wire grid 25 was made of silver plated copper wire of 5 to 10 mil thickness and suitably formed in a sinusoidal or corrugated configuration as illustrated in FIG. 1. The ends 26 and 27 of grid 25 are electrically connected for example by soldering to cup-shaped member 24 as illustrated by spaced apart joints 26 and 27. In FIG. 1, the corrugations of grid 25 extend from the bottom of cup-shaped member 24 to project to a height greater than the projected height of buttons 20, 21 and 22. Various other grid configurations and grid positioning may also be employed within the scope of this invention to provide the desired results. Leads 15, 16, 17 and 18 pass through suitable insulating material grommets 15',

Q 16', 17 and 18' respectively, of preferably nylon, which are positioned in cup 24. Grommets 16', 17 and 1b and their lead openings are located between ends 26 and 27 of grid 25.

With grid 25 in position as illustrated, the cup-shaped member 24 is filled with a suitable dielectric material 28 in a fluid or molten state. This dielectric material 28 completely fills the intervening spaces and imbeds wire grid 25 therein. The dielectric material also fills the space contained within the periphery of grid 25 but does not extend into full contact with the sides of cup member 24. A slight spacing is maintained at this point to alleviate expansion problems. As one preferred method of encapsulating, a thin wall tube is concentrically positioned in cup 24, and cup 24 filled with a fluid or viscous dielectric therethrough. When the tube is removed a space remains between the dielectric 28 and the wall of cup member 24. The dielectric may be chosen from various available resins, plastics, rubbers, etcetera, or, as in one preferred practice of this invention, silicone rubber of predetermined electrical insulation ability was employed.

Electrical shielding of terminals 20, 21 and 22 is completed by means of a further grid 29, as illustrated in FIG. 2. Grid 29 is made of fine wire similar to that of grid 25, and is placed across the top of cup-shaped member 24. More particularly, the ends of the grid wire 29 are suitably afiixed in opposed apertures 30 and 30' provided in the wall of cup-shaped member 24 to maintain the grid 29 in its illustrated position, which at this point is lying across the top of dielectric 28. Thereafter, a mixture of a dielectric such as 28 and an electrically conductive material such as carbon is pressed in a thin layer over grid 29* as an extra precautionary step. This latter mentioned dielectric may be different from dielectric material 28 for ease in handling, mixing with carbon etcetera. A small dish cover plate 31 is placed over the cup-shaped member 24 and sealed such as by soldering at its periphery with the periphery of cup member 24.

The bottom terminal of the magnetron 11 is also shielded as more clearly illustrated in FIG. 3. Referring now to FIG. 3, there is shown a bottom view of the magnetron assembly of FIG. 1. The bottom portion of magnetron assembly 10 includes a relatively shallow cup-shaped member 32 positioned in surrounding relationship to the magnetron ceramic body 11. Lead is illustrated as being electrically connected to terminal 33 which is imbedded in the ceramic material ring 34. Because of the shallowness of the cup member 32, it is preferred not to surround the electrode 33 by the use of a grid such as grid 25. It is more preferable merely to fill the shallow cup member 32 with a suitable dielectric material 28 as described with reference to cup 24 and to provide shielding means in a bottom cover 31' as illustrated in FIG. 4. Referring to FIG. 4, the bottom cover 31' isillustrated as having a fine wire grid 29' suitably electrically connected such as by soldering to the under surface of dish cover 31'. When cover 31 is placed in the position as illustrated in FIG. 1, grid 29' is forced into the plastic dielectric material 28. Because of the electrical connection of grid 29' to cover 31, and because of the electrical connection of cover 31' to cup member 32, the terminal 33 is sufficiently electrically shielded.

It is a necessary feature of this invention that for optimum operation the electrical shielding of the magnetron assembly 11 includes shielding of both the top terminals and bottom terminals, and also of a substantial length of the input leads 15-18 as known in the art. In the practice of this invention, substantially the entire length of leads 15-18 was coated with an electrically conductive resin for shielding purposes.

Practice of this invention in accordance with the teachings as given indicates excellent results with little if any arcing or corona discharge which would deleteriously affect frequency stabilization. One of the problems with a shielding material in the form of a dielectric mixed with electrical conductive particles is that the magnetron is subjected to different temperature variations such that the dielectric may or may not be in contact with the surrounding metal enclosure such as cup members 24 and 32 and thus when gaps appear, corona discharge or arcing occurs to affect frequency stabilization. By means of the grids and their particular use and positioning in the present invention, temperature effects are minimized. Practice of this invention is similarly applicable to various other R.F. apparatus employing exposed terminal portions including magnetrons and klystrons.

While this invention has been described with reference to particular and exemplary embodiments thereof, it is to be understood that numerous changes can be made by those skilled in the art without actually departing from the invention as disclosed, and it is intended that the appended claims include all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a voltage tunable magnetron device having a grounded metal casing containing exposed terminal connections for connection of electrical leads thereto the improvement comprising in combination,

(a) dielectric encapsulating means encapsulating said terminals and the-connecting portions of said leads in said casing,

(b) said encapsulation means including electrically conducting metal strand means imbedded therein in spaced relationship to said casing,

(c) said electrical conducting strand means including an electrically conducting wire grid surrounding said terminals between said terminals and said casing and electrically connected to said casing, and

(d) said encapsulating means being effective to bleed off electrical discharges to stabilize output of said electrical device.

2. A voltage tunable magnetron having electrical shielding means incorporated therewith comprising in combination,

(a) a magnetron casing assembly having exposed electrical terminals at opposite ends thereof with electrical input leads connected thereto,

(b) a cup-shaped metallic member surrounding the said terminals on each end of said magnetron,

(0) one of said cup-shaped members having peripherally spaced therewithin an electrically conductive wire grid surrounding said terminals and electrically connected to said cup-shaped member,

(d) a dielectric material filling each of said cup-shaped members and maintaining the grid in said spaced relationship,

(e) the other of said cup-shaped members having electrically conductive means in said dielectric material therewithin connected to its said cup-shaped member,

(f) and a metal dish cover electrically connected to and closing the top of each cup-shaped member,

(g) and sheilding means shielding said input leads.

3. The invention as recited in claim 2 wherein said dielectric is silicone rubber.

4. A voltage tunable magnetron having electrically shielding means incorporated therewith which comprises in combination,

(a) a magnetron cylindrical casing assembly having electrical terminals projecting from opposite ends. thereof,

(b) a cup-shaped metallic member surrounding the said terminals on each end of said magnetron,

(c) one of said cup-shaped members having peripherally spaced therewithin an electrically conductive 5 6 wire grid surrounding said terminals and electrically (h) and shielding means shielding said input leads. connected to said cup-shaped member, 5. The invention as recited in claim 4 wherein said (d) adielectric material filling each of said cup-shaped Wire grid is a Corrugated fine Wlfe 0f from about 5 members, to 10 mil thickness imbedded in silicone rubber. (e) the dielectric material in said cup-shaped mem- 5 bers being spaced from the Walls of cup-shaped References Cited by the Exammer members, UNITED STATES PATENTS (f) a pair of additional grids one of each positioned 2,377,153 5/1945 Hunter et al. 174-127 in each of said cup-shaped members to lie imbedded 2,813,922 11/ 1957 Arnold 313-318 across the top of the dielectric therein, 10 3,131,326 4/1964 Armstrong et al 3 1539 (-g) and a metal dish cover electrically connected to 3,223,831 v12/1965 Krugand closing the top of each cup-shaped member, said grids electrically connected to the casing, DAVID GALVIN Pnmmy Examiner 

1. IN A VOLTAGE TUNABLE MAGNETRON DEVICE HAVING A GROUNDED METAL CASING CONTAINING EXPOSED TERMINAL CONNECTIONS FOR CONNECTION OF ELECTRICAL LEADS THERETO THE IMPROVEMENT COMPRISING IN COMBINATION, (A) DIELECTRIC ENCAPSULATING MEANS ENCAPSULATING SAID TERMINALS AND THE CONNECTING PORTIONS OF SAID LEADS IN SAID CASING, (B) SAID ENCAPSULATION MEANS INCLUDING ELECTRICALLY CONDUCTING METAL STRAND MEANS IMBEDDED THEREIN IN SPACED RELATIONSHIP TO SAID CASING, (C) SAID ELECTRICAL CONDUCTING STRAND MEANS INCLUDING AN ELECTRICALLY CONDUCTING WIRE GRID SURROUNDING SAID TERMINALS BETWEEN SAID TERMINALS AND SAID CASING AND ELECTRICALLY CONNECTED TO SAID CASING, AND (D) SAID ENCAPSULATING MEANS BEING EFFECTIVE TO BLEED OFF ELECTRICAL DISCHARGES TO STABILIZE OUTPUT OF SAID ELECTRICAL DEVICE. 